Electric discharge device



April 5, 1960 R. J- SLOAN ETAL ELECTRIC DISCHARGE DEVICE Filed Feb. 28, 1957 COOLING FLUID SOURCE INVENTORSZ ROLLIN J. SLOAN LOUIS D. OWEN THEIR TTORN Y 2,931,935 ELECTRIC DISCHARGE nEvICE' Rollin J. Sloan and Louis D. Owen, Owensboro, Ky., as-

signors to General Electric Company, a corporation of New York Application February 28, 1957, Serial No. 643,112

1 Claim. (Cl. 313-631) Our invention relates to electric discharge devices and.

Often in this type of Additionally, in order to insure an evacuated condition 7 0f the envelope, it is necessary to provide'a vacuumtight seal between the lead and the envelope. Some of these seals have been found highlysensitive to excessive temperature variations and subject to failure due ,to thermal shock resulting from sudden or rapid tempermore changes, orsudden or rapid applications of exces' sive heat. 1 I I For example, during the usual outgassing and exhaust operations in the manufacture, of electric discharge devices of the presently considered type, the electrode supported in the envelope by the above-described type' of lead is subjected to relatively high temperatures in order to. remove occluded gases from the material thereof. This heating operation has heretofore often resulted in transfer to the lead of substantial quantities of heat which tended to efiect excessive expansion of the portion of the lead at the glass-to-rnetal seal and, thus, effect failure of that seal. Efforts to avoid such seal failure have involved structures wherein the electrode was supported from an internal portion of the lead by means of conductive elements of relatively small cross-section, thus to reduce the heat conductive path from theelectrode to that portion of the lead at the seal.-- This structure, however, did not provide a suitably rigid support for the electrode. In an effort to provide desired rigidity the lead was also constructed tubular; and to minimize the heat conductive path between the electrode and the seal in this type of structure the lead was constructed with a plurality of circumferentially arranged apertures. However, formation of leads with lateral apertures added substantially to the effort and expense of manufacturing the leads.

Accordingly, the primary object of the present invention is to provide new and improved structures whereby an electrode lead may be sealed in an envelope and whereby operations requiring substantial heating of the electrode may be carried out without deleteriously affecting the seal at the lead.

Another object of the present invention is to provide an electrode support and contact structure which accomplishes a rigid support for the electrode and is adapted for protecting a seal between that structure and an insulative envelope. I

Still another object of the present invention is to reduce substantially the manufacturing cost of electrode leads and minimize seal failures'during tube manufacture.

Further objects and advantages of our invention will become apparent as the following description proceeds and the features of novelty which characterize our invention will be pointed out with particularity in the claim annexed to and forming part of this specification.

In carrying out the objects of our invention we bond an electrode element to one end of a tubular lead and then we seal the lead through the dome portion of an insulative envelope of an electric discharge device. Thus, a vacuum-tight seal is provided between the envelope and lead, and the lead is efiective for supporting the electrode in the envelope. permitted to extend exteriorly of the envelope to provide an electrical contact for theelectrode. The tubular form of the lead minimizes the heat conduction path.

between the electrode and. seal while also effecting, substantially rigid support for the electrode. The electrode is then heated for effecting outgassing or any other operation and concurrently a controlled blast of cooling fluid is directed against the external portion of the lead. The internal end of the lead can be bonded completely about the circumference thereof to the electrode, in which case the end of the electrode is apertured to vent the interior of the lead through the electrode. In another form the electrode can be bonded to the lead at only" spaced intervals for reducing the heat transfer therebetween. in this form an insulative substance can be utilized between the contiguous surfaces of the lead and electrode. In this form also the electrode can be apertured to vent the lead. Additionally, the lead can be formed of a chromium alloy and the heat insulative substance can comprise a coating of chromium oxide thereon.

' For a better understanding of our invention, reference may be had to the accompanying drawing in which:

Fig. l is an enlarged, fragmentary, perspective and somewhat schematic illustration of equipment employable with oneform of our invention and ofan electric discharge device constructed to include one of the structural embodiments of our-invention;

Fig. 2 is ,an enlarged, fragmentary, perspective illustration of a modified form of our invention; and

Fig. 3 is an enlarged; fragmentary, sectional view of that form of our invention illustrated in Fig. 2.

Referring to Fig. 1 there is shown a half-wave rectifier. which embodies one form of our invention and which includes an insulative or glass envelope 1, a tubular anode 2 and a cathode K disposed in the anode.

bottomed construction with the open end extending downward for receiving the cathode structure.

The cathode K structure is supported on leads 3 sealed in and extending through an insulative stem 4- which, in

turn, is sealed in the lower end'of the bulb portion of the envelope thereby to complete the envelope. Additionally, the stem, in the illustrated stage of manufacture of the device, includes an exhaust tubulation 5 which is adapted for fitting in the chuck of a suitable exhaust head 6, thereby to afford communication between the head and the envelope for efiecting evacuation of the latter.

' The anode is supported in the envelope from the upper or dome portion thereof by a thin walled tubular anode lead or end cap 7. In the form of our invention illustrated in Fig. 1, the lead 7 is also of an inverted cup-like construction, thus to provide a closed outer end. The inner end of the lead 7 is solid-walled or imperforate and includes a circumferential flange 8 which is completely circumferentially bonded as at 9, and as by welding, to the flat bottom of the anode 2. The bottom portion of the anode includes an aperture 2A, the purpose for which will be brought out in detail hereinafter. Additionally,

Patented Apr. 5, 1960' A portion of the lead is The anode is of an inverted cup-like or bell-shaped, flatin order to facilitate the making of glassto-metal seals the lead 7 is formed of a chromium alloy such as a chromium-iron alloy. Following welding of the lead flange 8 to the anode the resultant assembly is fired at a temperatitre of approximately 1000 C. in a damphydrogen atmosphere whereby the lead including the undersurface portions of the flange 8 which are not directly welded to the anode become coated with chromium oxide, such as exaggeratedly illustrated at Sr: in Figure 1. This coating facilitates making of the glass-to-metal seal and, additionally, is heat insulating in nature and acts as a heat barrier between contiguous portions of the lead and anode for a purpose which will also be brought out in greater detail hereinafter. Additionally, chromium oxide is a relatively stable compound at high temperaturesv and will not break down during the outgassing step.

After the above-described sub-assembly of the lead and anode and oxidizing of the lead are accomplished we glass-to-metal seal the lead, as at 11, in the dome of the bulb portion of the envelope 1. Thus, the anode is rig.- idly supported in the envelope bulb with a portion of the lead 7 extending externally of the bulb.

Thereafter, the cathode-supporting stem is sealed to the bulb for completing the envelope. Following this sealing operation the tubulation is inserted in the exhaust head 6 in preparation for the exhaust and outgassing operations.

The outgassing operation involves heating the internal elements of the device including the anode to a substantially high temperature whereat occluded gases are released from the materials of these elements for evacuation thereof.

The heating step is accomplished inductively as by disposing the device in an energized radio frequency heating coil 12. During heating of the anode 2 heat tends to flow therefrom to the lead 7 which heat ordinarily would tend thermally to expand excessively the material of the lead 7 and thus crack the seal 11 whereby the device would be destroyed for its intended purpose. Additionally, the atmospheric content of the tubular lead 7 tends to expand when heated which would mechanically expand or bulge the side walls of the lead and also tend to crack the seal 11.

The above-mentioned heat flow from the anode to lead is impeded to some degree by the heat barrier formed by the chromium oxide 8a between contiguous portions of the anode and lead flange. Thus, thermal expansion of the lead is minimized.

In order further to minimize thermal expansion of the lead 7 during heating of the anode 2, we direct a blast of cooling fluid, and preferably air, against the upper portion of the lead, generally in the manner illustrated schematically in Figure 1, utilizing equipment such as that generally designated 13. It would be undesirable to cool the anode lead to a point where it does not expand thermally while the glass at the seal expands because this vould probably result in separation of the glass and metal. Therefore, we control the blast of cooling fluid so as to avoid excessive thermal expansion of the lead and to permit thermal expansion of the lead which corresponds substantially with the expansion of the glass at the seal.

The above-mentioned mechanical expansion of the lead 7 due to expansion of the gaseous contents thereof is avoided through the provision of the aperture or vent hole 2a in the flat bottom of the anode 2. This aperture avoids entrapment of any gas in the lead and permits expansion of gas from the lead into the greater volume of the envelope 1 through the anode.

Thus, we have provided a new and improved anode and lead assembly which is simple in construction, inexpensive to manufacture and which affords maximum rigid support for the anode. Additionally, it will be seen from the foregoing that we have provided a new and improved structure for use in etfectively outgassing an electric discharge device without deleteriously affecting the lead seals thereof.

Another embodiment of our anode and lead assembly is illustrated in Figs. 2 and 3. This assembly includes an anode 15 which can be identical to the anode 2 of Fig. 1, including an aperture 15a in the bottom thereof. In this assembly the lead 16 can be identical in material and construction to the lead 7 of Fig. l and is sealed in the dome of a bulb 17 at 18. in the same manner as the previously described embodiment. Here, however, a circular flange 19 on the lead 16 is welded to the bottom of the anode at only spaced intervals. Preferably we spot weld the flange to the anode at two points spaced 180 apart, as at 29. This manner of securing the lead and anode results in reduced heat transfer between these elef ments and thus minimizes the undesirable flow of heat from the anode toward. the seal. 18 during outgassing. The heat conduction path and heat exchange between the elements are minimized by virtue of spaces left between the elements in the regions between the spot welds. These spaces are small but are substantially effective as heat barriers.

Additionally, following Welding of the lead to the anode the assembly as fired in damp hydrogen in the above described manner and the lead, including the undersurface of the flange 19 becomes coated with chromium oxide, as exaggeratedly illustrated at 19a in Figs. 2 and 3. As pointed out above, this coating has heat-insulating properties and serves as a further heat barrier between the anode and lead. In the form of Figs. 2 and 3 this heat barrier is substantial due to the fact that it extends over the complete undersurface of flange 19 except only for the areas corresponding to the two spot welds.

We have found that suitable chromium oxide coatings can be obtained when the lead is formed of materials having substantially the following percentage compositions:

6% chromium, 42% nickel and the remainder iron 28% chromium and the remainder iron l7%- 1S% chromium and the remainder iron While the above-noted specific compositions have been found particularly adaptable to our specifically described form, other chrome-iron or chrome-iron-nickel will also serve satisfactorily to provide the desired stable and hcatinsulative chromium oxide coating.

Additionally, if desired, other heat-insulating materials may be disposed between the unwelded contiguous portions of the leadand anode.

During heating of the anode of Figs. 2 and 3 for outgassing in the manner described above, heat flow to the lead is impeded by the heat barrier 19a and by virtue of the fact that the spot welds afford only a relatively small direct heat conductance. Additionally, a controlled air blast is directed against the external end of the lead 16 to control thermal expansion thereof. Mechanical expansion of the lead due to expansion of the gas therein is minimized by escapage of such gas into the envelope through spaces between the spot welds and the aperture 151:.

' While we have shown and described specific embodiments of our invention, we do not desire our invention to be limited to the particular forms shown and de-. scribed, and we intend by the appended claim to cover all modifications within the spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

An electric discharge device having an envelope, elec' trodes within said envelope, a lead {or one of said elcc' trodes, said lead comprising a chromium alloy, said lead including a portion extending through the wall of said envelope and sealed directly thereto, said lead further including a flange disposed within said envelope, said flange being spot welded directly to one of said electrodes for effecting rigid support thereof, and the portions of said flange between the spot welds bearing a chromium oxide coating interposed between adjacent portions of said lead and said ohe electrode and diedtive for impeding heat transfer from fsaid one electrode to said lead and toward said seal.

References Cited in the file of-fthis patent UNITED STATES PAT ENTS Roensch May 27, 1924 Smith May 31, 1932 Pryslok May 10, 

